Diaphragm for loud speakers



June 19, 1928. 1,673,939

c. L. FARRAND DIAPHRAGM FOR LOUD SPEAKERS Filed Feb. 7, 1927 I INVENTOR v BY WM flan;

' ATTORNEYS Patented June 19, 1928.

CLAIR/L. FARRAND, OF FOREST HILLS, NEW YORK.

DIAPHRAGM FOR LOUD SPEAKERS.

Application filed February 7, 1927. Serial No. 166,296.

This invention relates to conical diaphragms for loud speakers.

It has been found that some conical diaphragms have a natural period of vibration due to the resonance chaniberformed by the concavity of the cone. For instance, a cone approximately 17 in diameter and about 2% in altitude will have a decided resonance in the neighborhood of approximately 300 cycles. This resonance makes the sound reproduction non-uniform throughout the sound gamutand sometimes results in blurring. It is the principal object of this invention to eliminate the natural period of vibration of the cone due to this cause, or at least alter it so that it does notztall within the gamut of audible frequencies.

It has been found that the natural period of vibration of the cone due to the above mentioned cause may be eliminated, or altered, so as to lie without the gamut of audible frequencies by sub-dividing or breaking up the space at the concave side of the cone into two or more spaces. A simple and etl'ective way of accomplishing this is to' provide the concave surface of the cone with one or more battles or partitions which extend inwardly toward the axis of the cone. Each bafiie should have one or more openings so that the battle will not form a completely enclosed compartment. The battle may be in the form of a frustum of a cone cemented at its larger base to the innersurface of the conical diaphragm so that the walls of the frustum ext-end inwardly toward the axis of the diaphragm. The free edge of thetrustum may be suitably reinforced as by reversely bending or creasing of the frustum.

The invention is illustrated in the accompanying drawings in which Figure l is a vertical longitudinal section of a conical diaphragm showing one battle applied to the concave side of the cone, the diaphragm in this figure being connected at its outer edge to an annular sounding board; Fig. 2 is a vertical longitudinal section of a conical diaphragm showing the use of two baflles at the concave side of the cone, the diaphragm in this figure being clamped at its edge in annular clamping rings; and Fig. 3 is a vertical longitudinal section of a conical diaphragm showing the application of the invention to a diaphragm which is not clamped-or rigidly's'upportedat its edge.

1 The conical diaphragm is shown at 1. It

the edge portion may be of the paper type commonly employed in present day loud speakers, or it may be made of any other suitable material. The partition or batlie comprises a frustum of a cone 2. (Figs. 1 and 3). The edge portion at the larger base of the frustum is bent-outwardly as shown at 3 so that it will lie substantially in the plane of the walls of the conical part of the diaphragm. The

bent brim portion 3 is cemented to the inner surface of the cone. so that the walls of the frustum 2 projectinwardly toward the axis of the cone. The free edge of the frustum 2 is preferably reinforced. This may be accomplished in a simple manner by bending the edge portion of the frustum inwardly as shown at 4. The frustum 2 may be made of paper or of any other suitable material. Satisfactory results have been obtained by using a frustum the walls of which have substantially the angularity shown in the drawings and the slant height of which is about one-fourth of the slantheight of the diaphragm-cone. \Vhen one battle is employed as in Figs. 1'and3 it may be positioned substantially in the position shown in the drawing.

In Fig. 2 two bafiies are employed, shown at 2 and 2". Each of the battles may be similar in construction to the single battle shown in Figs. 1 and 3. It may be desirable, however, where two or more battles are used to make the slant height of each frustuni slightly less than would be the case it only a single battle were employed. When a pluralityjof'baiiles are used, as in Fig. 2, they may be spaced apart equal or unequal distances along the inner face of the cone.-

Battles such as described above may be applied to the conicaldiaphragms of various types. It was for the purpose of illustrating the application of the invention to several types of conical diaphragms that the diaphragms in these figures were shown supported in different ways. In Fig.1 1 the conical diaphragm has a bent brim portion 5 which is cemented throughout a part of its length to a beveled seat 6 formed at the inner edge of an annular sound board 7 of wood or the like. In Fig. 2 the extreme edge portion 8 of the conical diaphragm is rigidly clamped between clamping rings 9, a bent brim'portion 10 being interposed between the cone of the diaphragm and the portion 8 which is clamped between the rings. In both Figs. 1 and 2 the purpose of the bent brim port-ion shown at 5 and 10 respectively is to permit the cone to vibrate freely in an axial direction.

In Fig. 3 the conical diaphragm is represented as being of the so-called free edge type in which the edge portion of the diaphragm is not rigidly held.

The actuating means for the diaphragm is not shown in the drawings as any suitable type of actuating device may be employed. The actuating device will be electromagnetic in the case of a radio loud speaker, and mechanical in the case of a phonograph. In either case. the actuatingdevice will be connected with the diaphragm so as to impart vibrations to its apex in the usual manner. All remaining details of construction that may be necessary to make up a complete loud speaker are not shown in the drawings as they have no bearing on the invention which relates to the diaphragm per so.

The bafiles or partitions, whether one or more be used, serve to subdivide or break up the space at the cancave side of the cone into two or more spaces. In this way the resonance chamber formed by the concavity of the cone is modified and the natural period of this original space is so broken up, altered or distributed that the resonance effect of the original spaceis eliminated or at least greatly diminished.

I claim r 1. The combination with a conical diaphragm of at least one baflle located at the concave side of the cone and positioned be tween the apex and the base of the cone to sub-divide the. resonance chamber formed by the concavity of the cone.

2. The combination with a conical diaphragm of a cone frustum secured to the inner wall of the cone between the apex and the base of the cone to sub-divide the resonance chamber formed by the concavity of the cone.

3. The combination with a conical diaphragm of a cone frustum located at the concave side of the cone and positioned between the apex and the base of the cone to sub-divide the resonance chamber formed by the concavity of the cone, said cone frustum having a bent brim-portion secured to the inner wall of the cone and having its free edge reinforced.

t. The combination with a conical diaphragm of a cone trustum located at the concave side. of the cone and positioned between the apex and the base of the cone to sub-divide the resonance chamber formed by the concavity ot the cone. said cone trustum having a bent brim portion secured to the inner wall of the cone and having its free edge bent to reinforce it.

5. The combination with a conical diaphragm of at least one battle located at the concavc side of the cone and. positioned betwcen the apex and the base of the cone, to

sub-divide the resonance chamber tormcd by the. concavity otthc cone, said balllc extending inwardly toward the axis of the cone and being provided with at least one opening.

6. The combination with a conical diaphragm of at least two battles located at the concave side of the cone and positioned between the apex and the base of the cone to sub-divide the rcsonam'c chamber formed by the concavity ot the cone. cach of said battles extending inwardly toward the axis of the cone and being provided with at least one opening. v

7. The combination with a conical diaphragm of at least one bafiic located at the concave side of the cone and positioned between the apex and the base of the cone to sub-divide the resonance chamber formcd by the concavity of the cone. said batlle extending inwardly toward the axis of the cone and being provided with a central opening.

8. The combination with a conical diaphragm of at least one battle located at the concave side of the cone and positioned between the apex and the base of the cone to sub-divide the resonance chamber formed by the eoncavityof the cone, said battle extending inwardly toward the axis of the cone and being provided with a central opening reinforced at its edge.

ture.

In testimony whereof I aflix my signa- 

